I suggest you ...

Create a sidewide double opt in management

This is really important for nearly anybody in the EU. We need a global deep implemented double opt in functionality. It should work like that:

Everytime a workflow is started, it should be checked if the contact opted in or not.

If we don't have an opt in, there should be a possibility to send an extra email, asking for opt in. But only if the contact actively filled out a form, providing its email adress. After getting the opt in, the workflow should be started.
If the contact already opted in, the workflow could be directly started

With the current solution, it's not possible to skip the double opt in process, if there is already an opt in.

The new anti spam legislation in Canada has made it mandatory to have lead submissions from landing pages and blog sign ups to "double opt in". We need a feature that automatically integrates this step between the initial submission and the addition of the lead to a list.

Every other autoresponder has already had this for years - I was astonished that it wasn't already in Hubspot. The suggested workarounds for this are too convoluted and fragile to use in the real world. Please get this implemented before one of your customers is subjected to the Canadian legal process.